The field of the invention relates generally to electric motors, and more specifically, to an end-shield and inner bearing cap assembly for use in an explosion proof electric motor.
The National Fire Protection Association (NFPA) publishes codes and standards, with the mission to minimize the possibility and effects of fire and other events. One NFPA standard is Standard No. 70, the National Electrical Code. Article 100 of Standard No. 70 includes a general definition of an explosion proof apparatus. Article 100 defines an explosion proof apparatus as, an “[a]pparatus enclosed in a case that is capable of withstanding an explosion of a specific gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby.” The explosion proof designation does not ensure that an apparatus is incapable of exploding, but rather that the apparatus is capable of withstanding an explosion without causing damage to the apparatus' surroundings beyond a certain level.
Flame paths positioned between a motor end shield and an inner bearing cap are known to minimize external damage in the event of an electric motor explosion. Another safety organization, Underwriters Laboratories (UL), publishes minimum requirements that must be met before receiving a UL rating. One minimum requirement established by UL for explosion proof motors is a minimum length of a flame path defined between a motor end shield and an internal bearing cap. Meeting/exceeding the minimum flame path length may prevent motor size reduction and/or limit the sizes of bearings that may be included in a motor.